KEVOS® MAKEOS · Power Transmission
Flat Belt Drive Design (Wrap, Tensions and Belt Width)
What belt length and wrap does this flat belt drive have, what are the belt tensions, and how wide must the belt be for its allowable stress?
Design of an open flat belt drive: wrap angle on the small pulley, belt length for the centre distance, belt speed, effective pull with a service factor, tight and slack side tensions with the centrifugal tension of the belt (as the belt drive tensions tool), the belt width needed so the tight-side stress stays within your allowable, and the shaft load.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Power | kW | Power transmitted. |
| Service factor | Service factor for the driven machine. | |
| Small pulley diameter | mm | Diameter of the small pulley. |
| Large pulley diameter | mm | Diameter of the large pulley. |
| Centre distance | mm | Distance between pulley centres. |
| Small pulley speed | rpm | Speed of the small pulley. |
| Friction coefficient | Friction coefficient between belt and pulley. | |
| Belt thickness | mm | Belt thickness. |
| Belt density | kg/m³ | Density of the belt material. |
| Allowable belt stress | MPa | Allowable tensile stress in the belt including joint efficiency (your value from the belt maker). |
| Belt width chosen | mm | Belt width considered. |
| Largest belt speed | m/s | Largest speed for the belt and pulleys. |
Method and formulas
- Wrap θ = 180° − 2 sin⁻¹[(D − d) ÷ 2C]; open belt length L = 2C + π(D + d) ÷ 2 + (D − d)² ÷ 4C.
- Effective pull F_e = P × SF ÷ v; centrifugal tension T_c = m v² with m = ρ b t; T₂ = F_e ÷ (e^{μθ} − 1) + T_c; T₁ = T₂ + F_e (as the belt drive tensions tool).
- Width so that T₁ ÷ (b t) ≤ σ_a: b = F_e e^{μθ} ÷ [(e^{μθ} − 1) t (σ_a − ρ v²)].
- Example: 7.5 kW at 12.147 m/s needs a 89.849 mm wide, 5 mm belt; the shaft load is 1,797.9 N.
Limitations
- Belt tension is assumed set so the drive just transmits the load with the service factor; real installation tension is often higher.
- Crossed belts and idlers change the wrap.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a flat belt for a fan, pump or line shaft
- Check a belt for a higher speed
- Find the shaft load for bearing selection
Who it is for
- Design engineers
- Maintenance engineers
- Power transmission engineers
What you get
- Wrap angle, belt length and speed
- Tensions and shaft load
- Belt width needed
Interpreting the result
- Above about 25–30 m/s centrifugal tension eats into the belt’s capacity.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2473–2520. Topic reference; no source tables or recommended settings are reproduced.
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Open the Flat Belt Drive Design (Wrap, Tensions and Belt Width) calculator
